Part 41 (1/2)
The labourers at the pumps relieved the monotony of their work, and shook off the cold, by taking a lively and talkative interest in the progress of the launch, and echoed the orders given them to pump with the 'big plunger,' or 'little plunger' of the pumps, or to 'fleet' the press. This and the singing of the gangs, which were constantly at work moving chains for the repair of the river tackle, or rolling logs of timber on to the ways to serve as pus.h.i.+ng-pieces for the presses, gave plenty of life to the operations; and then when the pressure had been got on the presses, and shouts from the bow and stern of the s.h.i.+p pa.s.sed the word that the river tackle was hauled taut, the order would be given to 'let go' the chain at one end of the s.h.i.+p. Immediately the rattling noise announced that this had been done, and, after a second or two of anxious watching, the s.h.i.+p slid off, the timbers, abutments, and pus.h.i.+ng-pieces creaking and groaning as the strain was suddenly relieved. While the s.h.i.+p was in motion, the whole of the ground forming the yard would perceptibly shake, or rather sway, on the discharge of the power stored up in the presses and their abutments. The appearance of the s.h.i.+p moving sideways in these short slips, when seen from the ways, was very imposing.
All these somewhat striking surroundings of the operations were naturally heightened in effect, when the work was being carried on in the early morning or late in the afternoon; and when the timber-framing and the groups of men at work were illuminated by the glare from the open fires which were kept burning near the pumps and presses.
The preparations already described were not completed till December 15.
In the meantime Mr. Brunel had been joined by his friend Mr. Robert Stephenson. Mr. Stephenson had not been aware of many vexatious circ.u.mstances which had even prevented Mr. Brunel from making full use of his own staff of a.s.sistants. Mr. Stephenson expressed to a common friend his regret that Mr. Brunel had not invited him down to the s.h.i.+p, and said that he should have gone down uninvited, but that he thought Mr. Brunel had reasons for not wis.h.i.+ng it. On the state of affairs being explained to him, Mr. Stephenson said, 'I'll go down to him at once;' he did so, and his arrival at Millwall was very welcome to Mr. Brunel.[169]
Mr. Stephenson agreed with Mr. Brunel as to the expediency of suspending operations until an ample excess of power was applied.
Fortified by the support of Mr. Stephenson, Mr. Brunel was prepared to advise the Directors to adopt this course; but, as the preparations for recommencing the work were just completed, it was determined to make a trial on the afternoon of December 15. The presses were all pumped up, and the river tackle hauled on; but, although the force applied was at least 300 or 400 tons greater than that which had last moved her, the s.h.i.+p did not yield, and the attempt was abandoned. After a careful consultation on the depressing result of this day's work, it was determined to make another attempt the next morning, in order to see if any new form of difficulty had arisen; and that after this operations should be suspended, and an ample number of additional presses provided.
The following day, December 16, as soon as Mr. Brunel and Mr. Stephenson had arrived, the pressure was again put on the presses, and the river tackle having been hauled taut, the chains at the bow were let go, and, to the great satisfaction of all present, the s.h.i.+p made a short slide.
The record of her movement showed that, although the adhesion was much greater, the r.e.t.a.r.ding force of friction was about the same as before, and that therefore there was no reason to a.s.sume the existence of any special obstacle. Another short slip was made; but, in getting up the pressure again, a press was burst, and the work was then stopped.[170]
Mr. Brunel's decision to suspend the launching operations at this point was approved at a meeting of the princ.i.p.al shareholders held the next day. His report to the Directors, and a memorandum of a verbal statement which he made to the meeting, are as follows:--
December 17, 1857.
In my letter of October 23, which was published at the time in the daily papers, I referred to the possible contingency of the power provided to move the vessel down the ways proving insufficient, and the operation then about to be attempted being so far unsuccessful; and, referring to what I considered a countervailing advantage in the absence of risk, I stated, 'the s.h.i.+p may stop half-way, or may not move at all, more power may have to be applied, but no injury to the s.h.i.+p can result from any failure in the course of proceeding in this mode of launching.'
The result has been that after moving the vessel nearly half the distance to low water, it has become necessary to increase very considerably the power which has effected this much, although it had already been much added to during the operation.
This will unavoidably be attended with some expense and delay, but not considerable, as the requisite hydraulic presses can be obtained ready made, and their application is simple, and the result cannot, I apprehend, be doubtful.
I do not mean to imply that I contemplated any such great increase of resistance as probable, such experiments as could be made before moving the s.h.i.+p having given me good reason to hope for a different result; but the possibility of it was contemplated, and I refer to this merely as explaining the statement I now make, that the difficulty is simply one of degree, of more or less power being required, and that nothing whatever has occurred to create any new cla.s.s of difficulty. The launching ways, about which anxiety had been expressed, and not unnaturally, have stood perfectly and without any settlement or any derangement by being pa.s.sed over.
There is no change of gradient or inclination in the ways capable of producing any effect, as has been supposed; the upper part of the ways having an inclination of 1025 inches per foot, and the lower part, where the s.h.i.+p now is, one of 1000 per foot, a difference too small to be appreciable, but which possibly by some mistake of figures may have led to the erroneous impression referred to.
The amount of resistance upon the ways in their present condition and inclination has now been positively ascertained, and an ample excess of power being applied, there can be no reason to doubt the result. I propose to apply that excess by going considerably beyond the amount which the calculation founded upon the results actually obtained would give as the maximum, and to double the power which has last moved the vessel.
_Memorandum of a verbal Report made to the Directors, and a small Meeting of the Princ.i.p.al Proprietors._
December 17, 1857.
That after full consideration of all the circ.u.mstances, and a.s.sisted by the best advice I could call in to my aid, namely, that of my friend Mr. Robert Stephenson, I considered that the only mode of proceeding, and one which there appeared no reason to doubt would succeed, was to apply considerably more press power; that I proposed to double what we had; that I believed I was able to put my hands upon the requisite presses; that the river tackle so far as it went might now be considered good, but that unfortunately we were obliged to take up the princ.i.p.al part of the chains, which with great kindness and liberality Messrs. Brown and Lenox had lent us, and were now peremptorily called upon to deliver up; but that with their a.s.sistance I could replace them....
A large number of presses were obtained, the owners for the most part lending them free of charge. Among these presses was the large one, with a 20-inch cylinder, which had been used for lifting the tubes of the Britannia Bridge.
On each of the ways were placed nine presses. The total sectional area of the cylinders at the forward cradle was 1,066 circular inches, and that of the cylinders at the after cradle was 1,358 circular inches; but the Britannia press was not to be worked to its full power, so the total area of the cylinders may be taken as 2,300 circular inches, or 1,800 square inches. The presses might be considered as good for at least 2 tons on the square inch; this gave a power of 4,500 tons, which, with the 1,000 tons due to gravity, gave 5,500 tons, or equal to nearly half the weight of the s.h.i.+p. The presses were now coupled together in groups, in order to ensure that an equal pressure should be brought on them; and to each of these groups an accurate pressure gauge was attached.
All the presses having been tested, it was determined to recommence the actual operation of launching on Tuesday, January 5.
So much of the water in the pipes had been frozen that it was eleven o'clock before the order was given to the men to pump. When at one group after another the pressure was shown to be one ton on the circular inch, the pumps were stopped. As the backing of the presses continued to yield slightly, a stroke or two of the handles had to be made from time to time, to keep up the required strain. For six minutes there was perfect silence, and then the s.h.i.+p moved, sliding down about 3 inches.